Glyphosate in acid form is relatively water-insoluble, and in order to achieve significant water solubility, glyphosate has generally been formulated as a salt.
Significant tonnages of formulations comprising glyphosate salts are applied throughout the world each year in a wide range of cropping situations and other situations calling for the control of unwanted foliage. The achievement of greater herbicidal efficacy is of great interest because it provides the option of more effective weed control or more efficient use of the active ingredient.
A wide variety of glyphosate salts have been described for example                Franz in U.S. Pat. No. 4,147,719 describes mono or di salts of glyphosate with alkaline metals, alkaline earth metals, ammonium or organic ammonium cations.        Teixeira in WO 8704712 describes dry particulate sodium and potassium salts of glyphosate.        Magin et al in U.S. Pat. No. 5,710,104 describes amine, alkali metal, alkylsulfonium alkylphosphonium, sulfonylamine and aminoguanidine salts of glyphosate.        Broadhurst et al in U.S. Pat. No. 4,431,594 describes sulfonium and sulfoxonium salts of glyphosate as well as phosphonium and substituted ammonium salts.        Jeffrey in DD218366 describes the trisodium salt of glyphosate.        Large in U.S. Pat. No. 4437874 describes tri-mixed alkylsulfonium salts of N-phosphonomethyl glycine.        Large in WO 8303608 describes tetrasubstituted ammonium salts of glyphosate.        Large in EP73574 describes phosphonium salts of glyphosate.        Prisbylla in EP115176 describes stannic salts of glyphosate.        Prisbylla in EP124351 describes mixed long-chain alkylammonium salts of glyphosate.        Gaughan in EP 369076 describes trisubstitued sulfonium and sulfoxonium salts of glyphosate.        Bakel in EP103055 describes isothiouronium diisothiouronium and diguanidinium salts of glyphosate.        
The glyphosate salts described above generally comprise a particular cation which is present in a mole ratio of at least 0.9:1 with glyphosate.
Commercially available formulations of glyphosate salts include the “Accord”, “Roundup”, “Roundup Ultra” and “Roundup Xtra” brands of Monsanto Company. These formulations contain glyphosate as the isopropylammonium salt. Monsanto's Roundup Geoforce brand contains glyphosate sodium salt and Roundup Dry contains glyphosate ammonium salt. The “Touchdown” brand of Zeneca, contains glyphosate trimethyl sulfonium salt.
The above commercial formulations of glyphosate all comprise particular low-molecular weight salt cations (generally of molecular weight less than 300) and a key criterion for selecting the salt in such a formulation is the capacity to achieve high loading levels of glyphosate (acid equivalent) in the formulation.
The herbicidal activity of glyphosate salts can be enhanced by adding a certain quantity of amphiphilic agents (including amphiphilic salts) to the formulation. According to Bryson et al in WO 2000032045, amphiphilic materials (including surfactants) can enhance the activity of a formulation comprising glyphosate salts by                decreasing the spray drop size and thereby minimizing rebound from a foliar surface        increasing the adhesion between a spray droplet and a foliar surface        reducing run-off of spray drops from a foliar surface        increasing the area of contact between a spray drop and a foliar surface and        enhancing the penetration of glyphosate from the droplet through the cuticle to reach internal leaf tissue.        
Amphiphilic agents may be identified by virtue of their capacity to cause one or more of the following phenomena:                formulation of micellar aggregates, at concentrations above the critical micellar concentration (CMC)        reduction of the contact angle between water and a leaf surface        reduction of the surface tension of an aqueous phase        stabilization of dispersed oily droplets in the aqueous phase        reduction of spray drop size.        
Amphiphilic agents which have been claimed to enhance the herbicidal efficacy of formulations comprising glyphosate salts include the following:                quaternary ammonium surfactant;        etheramine surfactants;        alkylether and amine surfactant combinations;        acetylenic diol and alkyl(poly)glycoside surfactant combinations;        lipophilic fatty amine ethoxylate surfactants;        alkoxylated amine surfactants;        alkyl polyglycoside agents;        secondary or tertiary alcohol surfactants;        silicone copolymer wetting agents and trialkylamine oxide or quaternary amine or trialkylbetaine surfactant combinations;        sorbitan fatty acid ester and amine, quaternary ammonium or alkylglycoside surfactant combinations;        surfactants derived from alkanethiols;        polyoxyalkylene trisiloxane surfactants;        super-wetting agents such as silicone-based and fluorocarbon-based surfactants;        supra-molecular aggregates formed by one or more amphiphilic salts having a glyphosate anion and cations derived by protonation of one or more polyamines or polyamine derivatives, each having at least two nitrogen-containing groups and a C6-C30 hydrocarbyl or acyl group;        supra-molecular aggregates comprising one or more amphiphilic salts having a glyphosate anion and cation derived by protonation of secondary or tertiary oily amines;        alkoxylated primary alcohol surfactants;        alkyl polysaccharide derivates;        alkyl polyglycoside and ethoxylated alcohol combinations;        alkylglucosides;        surfactants comprising polyhydroxyhydrocarbyl and amine functionality;        alkylglycoside and alkoxylated alkylamine surfactant combinations;        alkyldiamine tetraalkoxylate surfactants;        succinic acid derivatives;        alkoxylated amido amines;        sugar glycerides such as rapeseed oil sugar glyceride;        diamine surfactants;        widely-bridged alcohol polyethoxylates;        water-soluble long-chain hydrocarbyl dimethylamine oxides and quaternary ammonium halide combinations;        hydroxyalkylammonium adjuvants;        polyether diamine surfactants;        cationic, anionic, nonionic or zwitterionic silicone adjuvants;        organosilicone surfactants and diphenyl oxide sulfonate surfactant combinations;        a range of ether phosphate adjuvants;        phosphourous surfactant adjuvants;        polyglycerol and polyglycerol derivatives;        C8-C22 sarcosinate or sarcosinate salts;        ethoxylated vegetable oils;        polyethoxylated dialkylamine surfactants;        C10-C18 alkylpolyglycol ether sulfates; and        salts of fatty acids.        
Non-amphiphilic additives have also been claimed to enhance the bioefficacy of glyphosate, for example                Toussaint (EP498145) has described the use of an inorganic ammonium salt, preferably ammonium sulphate;        Hay (AU674464) has described the use of an alkyl-substituted ammonium sulfate;        Chamberlain (US5529975) has described the use of polyacrylamide;        Amakasa (JP2000026209) has described the use of ethanol;        Hioki (WO9701281) has described the use of oxalic acid, and lower molecular weight salts thereof.        